The present invention relates to hydrosilation catalysts which promote the addition of unsaturated epoxides to SiH-containing siloxanes and silanes. More particularly, the present invention relates to certain rhodium-based hydrosilation catalysts which promote the addition of unsaturated epoxides to SiH-containing siloxanes and silanes without promoting ring opening polymerization of the epoxide.
Epoxy-silicone monomers, oligomers, and polymers are usually prepared by a hydrosilation addition reaction between an olefin epoxide and a SiH-containing siloxane or silane in the presence of a platinum or platinum-based hydrosilation catalyst. Such reactions are described, for example, in copending, commonly assigned application Ser. No. 07/332,646, filed Apr. 3, 1989, and in U.S. Pat. No. 4,279,717 (Eckberg).
However, it has been found that in addition to catalyzing the olefin and SiH addition reaction, platinum catalysts also catalyze the ring-opening polymerization of the epoxide in the presence of SiH. Copending, commonly assigned application Ser. No. 07/473,802 (Riding et al.), filed Feb. 2, 1990, discloses the use of platinum or platinum-based catalysts to promote the ring opening of epoxides. The ring-opening polymerization of the epoxide during production of the epoxysilicone is undesirable because such polymerization causes the reaction mixture to gel completely, resulting in loss of the entire batch and in loss of considerable time in cleanup of the insoluble gelled resin.
In addition, partial ring opening polymerization can result in irreproducible batch-to-batch variations in the viscosity. Good viscosity control is essential in critical coating applications such as those involved in paper release coatings.
It has been observed that epoxy-silicone monomers stored in the presence of a platinum catalyst have a tendency to gel on standing due to slow ring opening polymerization at room temperature.
Thus far, epoxysilicone fluids have been successfully produced by careful control of batch temperature and olefin-epoxide feed rate during the synthesis and by sue of low levels of mercaptans, e.g., dodecyl mercaptan or 2-mercaptobenzothiazole, to de-activate platinum catalyst after the hydrosilation reaction. However, there remains sufficient possibility of the ring opening polymerization occurring that each batch could result in gelling of a large reactor.
The present invention is based on the discovery that certain rhodium-based catalysts are effective for promoting the addition of olefin-epoxides to SiH-containing siloxanes and silanes without promoting the ring opening polymerization of the epoxide starting material or final product.
The use of rhodium-based catalysts for promoting the hydrosilation of olefinic substrates which are not epoxy-functionalized is known in the art. Reference is made to J. F. Harrod and A. J. Chalk, in "Organic Syntheses via Metal Carbonyls", Vol. 2, I. Wender and P. Pino, editors, John Wiley, N.Y. 1977, pages 685-687; and J. L. Speier, Adv. in Organomet. Chem., Vol. 17, 407 (1979).
Hydrosilation reactions between olefinic epoxides and organohydrogenpolysiloxanes catalyzed with platinum metal complexes containing rhodium, ruthenium, palladium, osmium, and iridium are also known in the art. Reference is made, for example, to copending, commonly assigned application Ser. Nos. 07/332,646, filed Apr. 3, 1989, and Ser. No. 07/473,802, filed Feb. 2, 1990, and U.S. Pat. No. 4,279,717 (Eckberg).
It is therefore an object of the present invention to provide a method for preparing epoxysilicon compounds by means of a hydrosilation reaction between an unsaturated epoxide and an SiH-containing silicon compound in the presence of a hydrosilation catalyst which promotes the hydrosilation reaction without promoting the ring opening polymerization of the epoxide ring in either the unsaturated epoxide starting material or the epoxysilicon product.
It is another object of the present invention to provide a hydrosilation catalyst for the addition reaction between an unsaturated epoxide and a SiH-containing silicon compound to form an epoxysilicon compound, wherein the catalyst effectively promotes the hydrosilation reaction without promoting the ring opening polymerization of the epoxide ring in either the unsaturated epoxide starting material or the epoxysilicon product.
These objects and others are achieved in the present invention.